By her cute appearance and her voice, accompanied with her initial way of talking gives her the impression of being innocent and child-like. However, in her introduction alone, it is quickly revealed that she is cruel with a malicious side in how she crushes ants while telling Hinata that they make a satisfying popping noise if crushed right, and even invites him to join her. She also constantly judges others and patronises them with rude insults, with Tsumiki and Souda being the most common victims. She often takes a jab at Owari as well, though she, unlike Tsumiki or Souda, doesn't get frustrated but rather actually takes her pranks into serious consideration. For example, she calls Tsumiki "shitty bitch" and Togami "Mr. Porkfeet."

On the other hand, she loves Japan and its cuisune very much, and does show some innocent and child-like traits like her liking for gummy candy or konpeito. She is also prone to tears when humiliated, such as in Chapter 2 when Owari says something smells and it turns out to be coming from Saionji. She also seems to hate it when people don't side with her, such as in one of her Free-Time Events when she tries to get Hinata to go and beat up Souda with her. She also often passes off her crying as fake tears, though Hinata notes that it probably isn't true.

Before the whole despair incident, Saionji lived with her grandmother and is heir to the Saionji Clan, which is also the head of the school of traditional Japanese dance. Being the heir, many people were jealous of her to the point of bullying her, such as poisoning her food or putting needles in her shoes when she was a young child, amongst other horrible things. In addition, her grandmother, though she treated Saionji well, only cared about pride of the family, to the point where Saionji couldn't even see her own parents. Because of her past, she considers herself a part as the noble class, and everybody else as meager slaves.